Ferroelectric polarization and resistive switching characteristics of ion beam assisted sputter deposited BaTiO3 thin films

In this work, 150 nm thick polycrystalline BaTiO₃ (BTO) films were deposited on Pt/TiO₂/SiO₂/Si substrate by ion beam assisted sputter deposition technique. The bias voltage dependent resistive switching (RS) and ferroelectric polarization characteristics of Au/BTO/Pt devices are investigated. The devices display the stable bipolar RS characteristics without an initial electroforming process. Fittings to current–voltage (I–V) curves suggest that low and high resistance states are governed, respectively, by filamentary model and trap controlled space charge limited conduction mechanism, where the oxygen vacancies act as traps. Presence of oxygen vacancies is evidenced from the photoluminescence spectrum. The devices also display P–V loops with remnant polarization (P_r) of 5.7 μC/cm² and a coercive electric field (E_c) of 173.0 kV/cm. The coupling between the ferroelectric polarization and RS effect in BTO films is demonstrated.     

Large spontaneous Hall angle in [Co,CoFe/Pt] multilayer

We have quantitatively investigated the Hall effect in [Co, CoFe/Pt] multilayer films. The [Co, CoFe/Pt] multilayers exhibit large spontaneous Hall resistivity (ρ_H) and Hall angle (ρ_H/ρ). Even though the Hall resistivity in [Co, CoFe/Pt] multilayer films (2.7–4 × 10⁻⁷ Ω cm) is smaller than that of amorphous RE–TM alloy films which show large spontaneous Hall resistivity (<2 × 10⁻⁶ Ω cm), the Hall angle of multilayer (6–8%) is almost twice than that in amorphous rare earth–transition metal alloy films (∼3%). The Hall angle provides evidence of the effects of the exchange interaction of the Hall scattering. The exchange is between conduction electron spins and the localized spins of the transition metal. The large Hall angle of [Co, CoFe/Pt] multilayer can be considered due to the high spin polarization and high Curie temperature of Co and CoFe transition metal layers. Even though the role of interfaces and surfaces in the magnetic properties of multilayer films may dominate that of the bulk, the Hall effects in [Co, CoFe/Pt] multilayer may be mainly dominated by the bulk effect.     

Improvement of fatigue resistance on La modified BiFeO3 thin films

The effect of lanthanum (La) addition in BiFeO₃ (BFO) thin films deposited on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates prepared by soft chemical method was explained. Increasing La concentration promotes changes on structure, microstructure and dielectric/ferroelectric response of films. X-ray diffraction reveals that the films are free of preferred orientations and structural distortion. La addition promotes an increase in dielectric permittivity. The polarization switching and the fatigue behavior of the BFO films were significantly enhanced by the La concentration.     

Annealing temperature dependent on structural,optical and electrical properties of indium oxide thin films deposited by electron beam evaporation method

In the present work the influence of annealing temperature on the structural and optical properties of the In₂O₃ films deposited by electron beam evaporation technique in the presence of oxygen was studied. The deposited films were annealed from 350 to 550 °C in air. The chemical compositions of In₂O₃ films were carried out by X-ray photoelectron spectroscopy (XPS). The film structure and surface morphologies were investigated as a function of annealing temperature by X-ray diffraction (XRD) and atomic force microscopy (AFM). The structural studies by XRD reveal that films exhibit preferential orientation along (2 2 2) plane. The refractive index (n), packing density and porosity (%) of films were arrived from transmittance spectral data obtained in the range 250–1000 nm by UV–vis-spectrometer. The optical band gap of In₂O₃ film was observed and found to be varying from 3.67 to 3.85 eV with the annealing temperature.     

Growth-induced perpendicular magnetic anisotropy and clustering in NixPt1−x alloys

Polycrystalline and epitaxial (1 0 0), (1 1 0), and (1 1 1)-oriented Ni₃Pt, NiPt, and NiPt₃ films were deposited over a range of growth temperatures from 80°C to 700°C. Films grown at moderate temperatures (200–400°C) exhibit growth-induced properties similar to Co–Pt alloys: enhanced and broadened Curie temperature, perpendicular magnetic anisotropy and large coercivity. As in Co–Pt, the magnetic properties suggest a clustering of Ni into platelets on the growth surface, as the films are being grown. Unlike Co–Pt, however, NiPt films exhibit a strong orientational dependence of anisotropy and enhanced Curie temperature, possibly resulting from different types of surface reconstructions which affect the growth surface.     

Cation site environment in ultrathin TiOx films grown on Pt(1 1 1) probed by X-ray absorption spectroscopy at the Ti 2p edge

We present the results of a XAS experiment carried out at the Ti 2p edge on well-ordered TiO_x ultrathin films grown on the Pt(1 1 1) surface. XAS at the Ti 2p edge has been extensively applied to the study of Ti bulk compounds, particularly to the study of titania. According to the literature, the corresponding Ti 2p edge spectral shape is related to the stoichiometry and crystal field symmetry at the Ti sites. In the present study we aim at extending the potential of the XAS technique by discussing Ti 2p spectra obtained on several, dimensionally confined, TiO_x phases in the form of ultrathin films. One of the main features of these films is their high degree of structural order. Furthermore, the results of previous studies provide valuable information about the chemistry and structure of the films, so that we are able to analyse the current XAS data in detail and to compare them with the appropriate Ti 2p XAS data of bulk oxides. We find that in the case of ultrathin film with a fully oxidised Ti⁴⁺ stoichiometry, the Ti 2p XAS data display features that are very similar to the ones observed in related bulk systems. The XAS data of the reduced TiO_x films (with x < 2) show a rather different and specific shape. By comparing the experimental spectra with an atomic type of model calculation we show that the Ti 2p XAS profiles can be attributed mainly to stoichiometry-symmetry effects.     

Investigation of thermal sensitivity and radiation resistance of SiOx〈Ti〉 metal-dielectric films

In this investigation the composite SiO_x〈Ti〉 films were prepared by the thermal evaporation of a mixture of silicon oxide (SiO₂) and Тi powders. The optical transmission of the films in the IR spectral range and their temperature-sensitive properties are studied. By varying the contents of the metal in vaporizer and time of evaporation it is possible to obtain SiO_x〈Ti〉 layers with resistance (for monopixel of 0.8 × 1 mm) from tens kOhms to MOhms and a value of the temperature coefficient of resistance (TCR) is equal to −2.22% K⁻¹. IR spectrum of SiO_x〈Ti〉 film is characterized by a broad absorption band in the range of 8–12 μm which is associated with the Si–O–Si stretching mode.Investigations of the effect of gamma irradiation on SiO_x〈Ti〉 films have shown that their temperature-sensitive properties, in particular TCR does not change up to a dose of 10⁶ Gy.These results suggest that SiO_x〈Ti〉 films can be used as materials for production of radiation-resistant thermosensitive detectors operated in radiation fields of γ-radiation and combining functions of IR-absorption and formation of an electric signal.     

Growth mode of Pt1−xNix films biased dc-sputter-deposited on MgO(0 0 1)

A study is made by TEM, XRD and by measuring electrical/magnetic properties, of growth mode and properties of Pt_1−xNi_x alloy films deposited on MgO(0 0 1) at 250°C by dc-sputtering at 2.5–2.7 kV in Ar. A bias voltage V_s≤−160 V was applied to the substrate during deposition. It was confirmed that the Pt film was polycrystalline with the texture of Pt(1 1 1)/MgO(0 0 1) while the films of Pt_0.14Ni_0.86 and Pt_0.19Ni_0.81 were epitaxially grown with Pt–Ni(0 0 1)[1 0 0]/MgO(0 0 1)[1 0 0] similarly to the case of Ni/MgO(0 0 1). Thus the growth mode transformation between Pt–Ni(1 1 1)/MgO(0 0 1) and Pt–Ni(0 0 1)/MgO(0 0 1) may be induced at x less than 0.81 for Pt_1−xNi_x alloy films. The temperature coefficient of resistance TCR from 100 to 300 K of Pt_0.14Ni_0.86 films was estimated to be 0.0044–0.0053 K⁻¹ and saturation magnetization at 300 K to be 1.7–3.2 kG, respectively, while TCR of Pt films was estimated to be 0.0035–0.0048 K⁻¹.     

High-pressure dielectric studies of a novel hydrogen-bonded ferroelectric (NH4)2H2P2O6

The hydrostatic pressure effect on the dielectric properties of (NH₄)₂H₂P₂O₆ ferroelectric crystal was studied for pressures from 0.1 MPa to 360 MPa and for temperatures from 100 to 190 K. The pressure–temperature phase diagram obtained is linear with increasing pressure. The paraelectric–ferroelectric phase transition temperature decreases with increasing pressure with the pressure coefficient dT_c/dp=?5.16×10^?2 K MPa^?1. Additionally, the pressure dependences of Curie–Weiss constants for the crystal in paraelectric (C₊) and ferroelectric (C_?) phases are evaluated and discussed. The possible mechanism of paraelectric–ferroelectric phase transition is also discussed.     

Pulsed excimer laser ablation growth and characterization of Ba(Sn0.1Ti0.9)O3 thin films

Polycrystalline thin films of Ba(Sn_0.1Ti_0.9)O₃ were deposited on Pt coated silicon substrates by pulsed excimer laser ablation technique. The room temperature dielectric constant of the Ba(Sn_0.1Ti_0.9)O₃ films was 350 at a frequency of 100 kHz. The films showed a slightly diffused phase transition in the range of 275–340 K. The polarization hysteresis behavior confirmed the ferroelectric nature of the thin films. Remanent polarization (P_r) and saturation polarization (P_s) were 1.1 and 3.2 μC/cm², respectively. The asymmetric capacitance–voltage curve for Ba(Sn_0.1Ti_0.9)O₃ was attributed to the difference in the nature of the electrodes. Dispersion in both the real (ε′_r) and imaginary (ε″_r) parts of the dielectric constant at low frequencies with increase in temperature was attributed to space charge contribution in the complex dielectric constant.     

Ti/CeOx(111) interfaces studied by XPS and STM

Low coverage of Ti was deposited on the well-ordered CeO_x(111) (1.5 < x < 2) thin films grown on Ru(0001) by physical vapor deposition at room temperature. The structure and interaction of Ti/ceria interfaces were investigated with X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) techniques under ultrahigh vacuum conditions. XPS data indicate that the deposition of Ti on both oxidized and reduced ceria surfaces causes the partial reduction of Ce from + 4 to + 3 state. Ti is formally in the + 4 state. STM data show the formation of small atomic-like titania features at 300 K, which coalesce to form chain structures upon heating. It is demonstrated in the study that the deposition of Ti can form mixed metal oxides at the interface and modify both electronic and structural properties of the ceria support. The structural study of Ti/ceria interfaces can be a key for understanding the higher catalytic activity of the Ti–CeO_x mixed oxide catalysts as compared with the individual pure oxides.     

Promotion effect of Pt on a SnO2–WO3 material for NOx sensing

Metal-oxide nanocomposites were prepared over screen-printed gold electrodes to be used as room-temperature NO_x (nitric-oxide (NO) and nitrogen dioxide (NO₂)) sensors. Various weight ratios of SnO₂–WO₃ and Pt loadings were used for NO sensing. The sensing materials were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface analysis. The NO-sensing results indicated that SnO₂–WO₃ (1:2) was more effective than other materials were. The sensor response (S=resistance of N₂/resistance of NO=R_N2/R_NO) for detecting 1000 ppm of NO at room temperature was 2.6. The response time (T₉₀) and recovery time (TR₉₀) was 40 s and 86 s, respectively. By further loading with 0.5% Pt, the sensor response increased to 3.3. The response and recovery times of 0.5% Pt/SnO₂–WO₃ (1:2) were 40 s and 206 s, respectively. The linearity of the sensor response for a NO concentration range of 10–1000 ppm was 0.9729. A mechanism involving Pt promotion of the SnO₂–WO₃ heterojunction was proposed for NO adsorption, surface reaction, and adsorbed NO₂ desorption.     

Ultrathin Y2O3(111) films on Pt(111) substrates

The growth of ultrathin films of Y₂O₃(111) on Pt(111) has been studied using scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), and low energy electron diffraction (LEED). The films were grown by physical vapor deposition of yttrium in a 10^? 6 Torr oxygen atmosphere. Continuous Y₂O₃(111) films were obtained by post-growth annealing at 700 °C. LEED and STM indicate an ordered film with a bulk-truncated Y₂O₃(111)–1 × 1 structure exposed. Furthermore, despite the lattices of the substrate and the oxide film being incommensurate, the two lattices exhibit a strict in-plane orientation relationship with the [11?0] directions of the two cubic lattices aligning parallel to each other. XPS measurements suggest hydroxyls to be easily formed at the Y₂O₃ surface at room temperature even under ultra high vacuum conditions. The hydrogen desorbs from the yttria surface above ~ 200 °C.     

Growth,structure, and thermal stability of epitaxial BaTiO3 films on Pt(111)

The growth of epitaxial ultrathin BaTiO₃ films upon rf magnetron sputter deposition on a Pt(111) substrate has been studied by scanning tunnelling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. The BaTiO₃ films have been characterized from the initial stages of growth up to a film thickness of 4 unit cells. The deposited films develop a long-range order upon annealing at 1050 K in UHV. In the submonolayer regime a wetting layer is formed on Pt(111). Thicker films reveal a Stranski–Krastanov-like structure as observed with STM. By XPS a good agreement of the thin film stoichiometry with BaTiO₃ single crystal data is determined. Due to annealing at 1150 K BaTiO₃ forms large two-dimensional islands on the Pt(111) substrate. Different surface structures develop on the islands depending on the O₂ partial pressure during annealing.     

Effects of Zr/Ti ratio on dielectric and ferroelectric properties of 0.8Pb(ZrxTi1−x)O3–0.2Pb(Co1/3Nb2/3)O3 ceramics

The influences of Zr/Ti ratio on electrical properties of the 0.8Pb(Zr_xTi_1−x)O₃–0.2Pb(Co_1/3Nb_2/3)O₃ ceramics prepared by a mixed-oxide method (with x = 0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary composition in this system. With XRD analysis, the crystal structure of dense specimens appeared to change gradually from tetragonal to rhombohedral with increasing Zr content. The dielectric properties measurements showed a maximum dielectric constant at x = 0.50, while the transition temperature decreased with increasing Zr content in the system. Moreover, all ceramics showed diffused phase transition behaviors with a minimum diffusivity at x = 0.50. In addition, the Polarization–Electric field (P–E) hysteresis loops of the ceramic systems also changed significantly with the Zr content. Interestingly, the loop squareness parameter reached maximum around x = 0.50. Other ferroelectric hysteresis parameters showed noticeable change at x = 0.50. These results clearly showed the significance of Zr/Ti ratio in controlling the electrical properties of the PZT–PCN ceramic systems.     

Characterization of LSGM films obtained by electrophoretic deposition (EPD)

The application of the electrophoretic deposition (EPD) technique to the preparation of high quality electrolyte films for intermediate temperature solid oxide fuel cells (IT-SOFCs) was investigated. Films of La_0.83Sr_0.17Ga_0.83Mg_0.17O_2.83 (LSGM) were deposited on Pt and La_0.8Sr_0.2MnO₃ (LSM) substrates from suspensions in acetone/ethanol (3:1 by volume) mixture solvent and sintered at 1300 °C. Pt supported LSGM films, 10–20 μm thick, exhibited good adhesion to the Pt substrate, well-distributed microporosity and some surface roughness. LSM supported films exhibited cracking after sintering at 1300 °C for 3 h. Up to 900 °C the bulk conductivity of the Pt supported LSGM film showed the same behaviour of LSGM pellet (E_a = 0.93 eV and 0.99 eV, respectively). The LSGM film exhibited lower bulk electrical conductivity than the latter (4.1 × 10^− 3 and 4.4 × 10^− 2 Ω^− 1 cm^− 1, respectively, at 700 °C). This difference should be ascribed to the slight Ga depletion in the LSGM film. An important issue remains the selection of adequate electrode for LSGM electrolyte films.     

Influence of substrate temperature on physical properties of sprayed Zn0.85Mn0.15O films

Zn_1−xMn_xO thin films have been synthesized by chemical spray pyrolysis at different substrate temperatures in the range, 250–450 °C for a manganese composition, x = 15%, on corning 7059 glass substrates. The as-grown layers were characterized to evaluate their chemical and physical behaviour with substrate temperature. The change of dopant level in ZnO films with substrate temperature was analysed using X-ray photoelectron spectroscope measurements. The X-ray diffraction studies revealed that all the films were strongly oriented along the (0 0 2) orientation that correspond to the hexagonal wurtzite structure. The crystalline quality of the layers increased with the increase of substrate temperature up to 400 °C and decreased thereafter. The crystallite size of the films varied in the range, 14–24 nm. The surface morphological studies were carried out using atomic force microscope and the layers showed a lower surface roughness of 4.1 nm. The optical band gap of the films was ∼3.35 eV and the electrical resistivity was found to be high, ∼10⁴ Ω cm. The films deposited at higher temperatures (>350 °C) showed ferromagnetic behaviour at 10 K.     

Memory characteristics and tunneling mechanism of Pt nano-crystals embedded in HfAlOx films for nonvolatile flash memory devices

A non-volatile flash memory device based on metal oxide semiconductor (MOS) capacitor structure has been fabricated using platinum nano-crystals(Pt–NCs) as storage units embedded in HfAlO_x high-k tunneling layers. Its memory characteristics and tunneling mechanism are characterized by capacitance–voltage(C–V) and flat-band voltage-time(ΔV_FB-T) measurements. A 6.5 V flat-band voltage (memory window) corresponding to the stored charge density of 2.29 × 10¹³ cm⁻² and about 88% stored electron reserved after apply ±8 V program or erase voltage for 10⁵ s at high frequency of 1 MHz was demonstrated. Investigation of leakage current–voltage(J–V) indicated that defects-enhanced Pool-Frenkel tunneling plays an important role in the tunneling mechanism for the storage charges. Hence, the Pt–NCs and HfAlO_x based MOS structure has a promising application in non-volatile flash memory devices.     

Effect of nitrogen partial pressure on Al–Ti–N films deposited by arc ion plating

AlTiN films with different nitrogen partial pressures were deposited using arc ion plating (AIP) technique. In this study, we systematically investigated the effect of the nitrogen partial pressure on composition, deposition efficiency, microstructure, macroparticles (MPs), hardness and adhesion strength of the AlTiN films. The results showed that with increasing the nitrogen partial pressure, the deposition rate exhibited a maximum at 1.2 Pa. Results of X-ray photoelectron spectroscopy (XPS) analysis revealed that AlTiN films were comprised of Ti–N and Al–N bonds. XRD results showed that the films exhibited a (1 1 1) preferred growth, and AlTi₃N and TiAl_x phases were observed in the film deposited at 1.7 Pa. Analysis of MPs statistics showed MPs decreased with the increase in the nitrogen partial pressure. In addition, the film deposited at 1.2 Pa possessed the maximum hardness of 38 GPa and the better adhesion strength.     

A novel selenization technique for fabrication of superconducting FeSex thin film

A combinative method with reactive sputtering deposition and selenization technique was applied to prepare superconducting FeSe_x films on LaAlO₃ substrates successfully. The influence of selenizing temperature on film components was studied. FeSe_0.96 and FeSe films had similar and good performances in transport measurement but little difference in magnetic property. The critical onset temperature got to 11.2 K and T_c,0 got to 4 K approximately. X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy were used to analyze the ratio of constituents and morphology of several selenized films. FeSe_x film had a porous structure on surface and no well preferred orientation, which were confirmed to have little influence on superconducting properties.